The human eye is a photosensitive organ that focuses and converts light into electrical impulses. The human eye is a slightly asymmetrical globe, roughly an inch in diameter, with the size differing by only a few millimeters among adults. The eye consists of two parts. The smaller front section of the eye comprises the iris, cornea, pupil, sclera, and the lens. The iris is the pigmented area of the eye that surrounds the pupil, which is a black circular opening that allows light into the eye. The sclera is the white area surrounding the iris. The iris, sclera, and pupil are covered by a clear dome called the cornea. Located behind the pupil is a lens, which focuses light to the back of the eye.
The back of the eye consists of a large chamber. The inside lining of the chamber is covered by a network of light sensing cells that are collectively called the retina. Leading posteriorly away from the eye is the optic nerve. Light enters through the pupil and is focused by the lens to the retina. The retina converts the light into electrical impulses, which are then transmitted to the brain via the optic nerve.
The eye is positioned in the orbit, which is a cavity or socket of the skull. Seven bones conjoin to form the orbital structure and together are shaped like a quadrilateral pyramid. The eye is essentially suspended within the orbit and there are six muscles of the orbit that attach to the eye to facilitate movement. The lateral and medial canthal tendons attach the eyelids to the orbital rim and prevent the eye from having any forward displacement away from the eye socket.
There are many circumstances in which the eyes may be damaged, resulting in a loss of vision. A blunt impact to the eye may potentially damage the structures located in the “front” of the eye (such as the cornea, sclera, iris and lens) or to the back of the eye (the retina and the optic nerve). When a blunt impact to the eye occurs a hematoma may form. A hematoma, or localized collection of blood outside blood vessels, may develop in the tissue surrounding the eye and is commonly referred to as a “black eye.” With minor injuries like a black eye, pooled blood usually drains towards the bottom of the eye after several days and no loss of vision occurs.
However, in some situations a blunt force can cause an orbital hemorrhage. A hemorrhage, in contrast with a hematoma, generally refers to a broken and bleeding blood vessel. The bleeding may occur internally or externally. In an orbital hemorrhage, the post-septal orbital space located behind the eye can accumulate blood, building pressure behind the eye. As discussed above, the orbital space is formed from seven bones that shape the socket and therefore, the accumulation of blood cannot expand posteriorly. As a result, anterior expansion occurs, causing proptosis (the forward displacement of the eye). Essentially, as the orbit fills with blood, the eye is pushed forward and out of the eye socket. However, the eye is tethered by the optic nerve and various tendons (including the lateral and medial canthal tendons). As pressure builds, the ophthalmic artery, which supplies oxygenated blood to all structures within the orbit, is compromised and results in a vision-threatening, acute orbital compartment syndrome (OCS). The optic nerve may also be damaged by the direct pressure of the fluid building in the orbit and the compression of the vascular supply to the optic nerve. In addition, the retina may be damaged by prolonged retinal ischemia (restriction of blood supply to the retina). Without prompt and proper care, the optic nerve and the retina may be damaged beyond recovery in as little as 90-120 minutes.
To treat acute OCS, orbital decompression must take place in order to avoid damage to sensitive orbital contents, like the optic nerve. The most common method of orbital decompression is by preforming a canthotomy and cantholysis of the inferior lateral canthal tendon that secures the lower eyelid to the orbital rim and prevents forward displacement of the eye.
In ideal situations, an ophthalmologist will perform the procedure in a hospital or other emergency medical facility. However, in many cases due to the time sensitive nature of the injury, many emergency room physicians have to perform a lateral canthotomy and cantholysis without an ophthalmologist.
In military or combat situations in remote areas, an ophthalmologist, hospital, or other emergency medical facility is likely unavailable. Due to the importance of prompt medical care to avoid any lasting damage to the patient's vision, the proper training of medical personnel would be beneficial to give on-site treatment in remote areas.